Methylphenidate is a psychostimulant which is a chain substituted amphetamine derivative. Similar to amphetamine and cocaine, methylphenidate targets the central nervous system, specifically the dopamine transporter (DAT) and norepinephrine transporter (NET). Methylphenidate is thought to act by increasing the concentrations of dopamine and norepinephrine in the synaptic cleft, as methylphenidate has both dopamine transporter (DAT) and norepinephrine transporter (NET) binding capabilities. Although an amphetamine derivative, the pharmacology of methylphenidate and amphetamine differ, as amphetamine is a dopamine transport substrate whereas methylphenidate works as a dopamine transport blocker. As a norepinephrine and dopamine re-uptake inhibitor, methylphenidate thus blocks re-uptake of dopamine and norepinephrine (noradrenaline) into presynaptic neurons (and possibly stimulates the release of dopamine from dopamine nerve terminals at high doses), thereby increasing the levels of dopamine and norepinephrine in the synapse. In some in vitro studies, methylphenidate has been shown to be more potent as an inhibitor of norepinephrine uptake/re-uptake when compared to dopamine. However, some in vivo studies have indicated that methylphenidate is more potent in potentiating extracellular dopamine concentrations than norepinephrine concentrations. Unlike amphetamine, it has been suggested in the scientific and/or clinical research community that methylphenidate does not seem to significantly facilitate the release of these two monoamine neurotransmitters at therapeutic doses.
Four isomers of methylphenidate are known to exist: d-erythro-methylphenidate, l-erythro-methylphenidate, d-threo-methylphenidate, and I-threo-methylphenidate. Originally, methylphenidate was marketed as a mixture of two racemates, d/l-erythro-methylphenidate and d/l-threo-methylphenidate. Subsequent research showed that most of the desired pharmacological activity of the mixture is associated with the threo-isomer resulting in the marketing of the isolated threo-methylphenidate racemate. Later, the scientific community determined that the d-threo-isomer is mostly responsible for the stimulant activity. Consequently, new products were developed containing only d-threo-methylphenidate (also known as “d-threo-MPH”).
Stimulants, including methylphenidate (“MPH”), are believed to enhance the activity of the sympathetic nervous system and/or central nervous system (CNS). Stimulants such as MPH and the various forms and derivatives thereof are used for the treatment of a range of conditions and disorders predominantly encompassing, for example, attention deficit hyperactivity disorder (ADHD), attention deficit disorder (ADD), obesity, narcolepsy, appetite suppression, depression, anxiety and/or wakefulness.
Methylphenidate is currently approved by the United States Food and Drug Administration (“FDA”) for the treatment of attention-deficit hyperactivity disorder and narcolepsy. Methylphenidate has also shown efficacy for some off-label indications that include depression, obesity and lethargy. In some embodiments, the prodrugs of the present technology may be administered for the treatment of attention-deficit hyperactivity disorder and narcolepsy, or any condition that requires the blocking of the norepinephrine and/or dopamine transporters.
Attention deficit hyperactivity disorder (ADHD) in children has been treated with stimulants for many years. However, more recently, an increase in the number of prescriptions for ADHD therapy in the adult population has, at times, outperformed the growth of the pediatric market. Although there are various drugs currently in use for the treatment of ADHD, including some stimulants and some non-stimulant drugs, methylphenidate (commercially available from, for example, Novartis International AG (located in Basel, Switzerland) under the trademark Ritalin®) is commonly prescribed. Moreover, during classroom trials, non-stimulants have shown to be less effective in improving behavior and attention of ADHD afflicted children than amphetamine derivatives.
Behavioral deterioration (rebound or “crashing”) is observed in a significant portion of children with ADHD as the medication wears off, typically in the afternoon or early evening. Rebound symptoms include, for example, irritability, crankiness, hyperactivity worse than in the un-medicated state, sadness, crying, and in rare cases psychotic episodes. The symptoms may subside quickly or last several hours. Some patients may experience rebound/crashing so severe that treatment must be discontinued. Rebound/crashing effects can also give rise to addictive behavior by enticing patients to administer additional doses of stimulant with the intent to prevent anticipated rebound/crashing negative outcomes and side effects.
Stimulants, such as methylphenidate and amphetamine, have been shown in the conventional art to exhibit noradrenergic and dopaminergic effects that can lead to cardiovascular events comprising, for example, increased heart rate, hypertension, palpitations, tachycardia and in isolated cases cardiomyopathy, stroke, myocardial infarction and/or sudden death. Consequently, currently available stimulants expose patients with pre-existing structural cardiac abnormalities or other severe cardiac indications to even greater health risks and are frequently not used or used with caution in this patient population.
Methylphenidate, like other stimulants and amphetamine derivatives, can become addictive and is prone to substance abuse. Oral abuse has been reported, and euphoria can be achieved through intranasal and intravenous administration.
Dependence on stimulants like cocaine can occur even after usage for a very short period of time due to their potent euphoric effects. For example, early signs of cocaine dependence include difficulty to abstain from cocaine use when it is present or available. Many stimulants including cocaine have a short elimination half-life and thus require frequent dosing to maintain the “high”. Chronic use of supratherapeutic doses of such stimulants may result in numerous mental and/or physical problems. Effects on mood may include anxiety, restlessness, feelings of superiority, euphoria, panic, irritation, and fearfulness. Behavioral symptoms include but are not limited to being extremely talkative, having increased energy, stealing or borrowing money, erratic or odd behavior, violence, lack of participation in activities that were once enjoyable, and reckless and risky behaviors. Examples of physical symptoms of stimulant dependence may include one or more of the following: decreased need to sleep, headaches, nosebleeds, hoarseness, increased heart rate, muscle twitches, malnutrition, increase in body temperature, nasal perforation, abnormal heart rhythms, chronic runny nose, constricting blood vessels, increased heart rate, increased blood pressure, sexual dysfunction, decreased appetite, dilated pupils, risks for contracting Human Immunodeficiency Virus (HIV), hepatitis C and other bloodborne diseases, gangrene of the bowel, cravings, and tremors. Examples of psychological symptoms of stimulant dependence may include one or more of the following: severe paranoia, violent mood swings, break from reality, lack of motivation, psychosis, hallucinations, inability to use sound judgment, and the rationalization of drug use. There is a variety of factors that can trigger or play a role in stimulant use disorder or stimulant dependence. Generally, these factors can be placed into three categories: genetic, biological, and environmental. Research has shown that individuals who have relatives with addiction problems are more likely to develop an addiction including cocaine dependence. The likelihood of becoming stimulant dependent is higher if the relative is a parent. Changes in brain function may be a biological factor that correlates with addiction problems. For example, low dopamine levels in the brain may result in an individual to abuse substances with the goal to attain pleasurable feelings. Environmental factors include but are not limited to unpredictable situations in the home lives of an individual; stressors, such as child abuse, the loss of a loved one, or other traumatic events. There is a need in the art for forms of methylphenidate that have a slow gradual increase in methylphenidate blood/brain concentrations until peak concentrations are achieved, or a slow gradual decrease of methylphenidate blood/brain concentrations after peak concentrations, or both. Not wishing to be bound by any particular theory, it is possible that slow onset of stimulant concentrations can decrease cardiovascular side effects, and slow elimination can decrease rebound effects. It has also been suggested that a larger increase in synaptic dopamine per time unit (i.e., higher rate of dopamine increase) results in more robust and intense euphoric effect. A slow increase in methylphenidate brain concentration produces a low rate of increase in synaptic dopamine and thus, may result in less rewarding and reinforcing effects. Without wishing to be bound by any particular theory, it has also been suggested that high occupancy of dopamine transporter receptors may decrease the rewarding and reinforcing effects of additional doses of stimulants like cocaine. This could be accomplished, for example, by repeated administration of large doses of a form of methylphenidate with a slow onset that does not result in euphoria.
There is also a need in the art for forms of methylphenidate that can provide a more rapid onset of methylphenidate blood/brain concentrations. Not wishing to be bound by any theory, certain indications may require a large and fast initial spike in blood and/or brain concentration of methylphenidate to provide to the subject sufficient efficacy, while other indications may require lower blood/brain concentrations of methylphenidate, but a small therapeutic amount of a form of methylphenidate with rapid onset may still be beneficial to provide fast efficacy when needed.
There is a further need in the art for forms of methylphenidate that can provide flexibility in dosing regimens. For example, a single daily dose form of methylphenidate in a composition that can provide both immediate and extended release PK profiles would be highly desirable.
There is an additional need in the art for forms of methylphenidate that can maintain the pharmacological benefit when administered, in particular via the oral route, but which preferably have no or a substantially decreased pharmacological activity when administered through injection or intranasal routes of administration.